The search for new therapeutic agents has been greatly aided in recent years by better understanding of the structure of enzymes and other biomolecules associated with target diseases. One important class of enzymes that has been the subject of extensive study is the protein kinases. Many diseases are associated with abnormal cellular responses triggered by protein kinase-mediated events. These diseases include autoimmune diseases, inflammatory diseases, neurological and neurodegenerative diseases, cancer, cardiovascular diseases, allergies and asthma, Alzheimer's disease or hormone-related diseases. Accordingly, there has been a substantial effort in medicinal chemistry to find protein kinase inhibitors that are effective as therapeutic agents.
Glycogen synthase kinase-3 (GSK-3) is a serine/threonine protein kinase comprised of α and β isoforms that are each encoded by distinct genes (Coghlan et al., Chemistry & Biology, 7, 793-803 (2000); Kim and Kimmel, Curr. Opinion Genetics Dev., 10, 508-514 (2000)). The threonine/serine kinase glycogen synthase kinase-3 (GSK-3) fulfills a pivotal role in various receptor-linked signalling pathways (Doble, B W, Woodgett, J R J. Cell Sci. 2003, 116:1175-1186). Dysregulation within these pathways is considered a crucial event in the development of several prevalent human disorders, such as type II diabetes (Kaidanovich O, Eldar-Finkelman H, Expert Opin. Ther. Targets, 2002, 6:555-561), Alzheimer's disease (Grimes C A, Jope R S, Prog.Neurobiol. 2001, 65:391-426), CNS disorders such as manic depressive disorder and neurodegenerative diseases, and chronic inflammatory disorders (Hoeflich K P, Luo J, Rubie E A, Tsao M S, Jin O, Woodgett J, Nature 2000, 406:86-90). These diseases may be caused by, or result in, the abnormal operation of certain cell signalling pathways in which GSK-3 plays a role.
GSK-3 has been found to phosphorylate and modulate the activity of a number of regulatory proteins. These proteins include glycogen synthase which is the rate limiting enzyme necessary for glycogen synthesis, the microtubule associated protein Tau, the gene transcription factor β-catenin, the translation initiation factor e1F2B, as well as ATP citrate lyase, axin, heat shock factor-1, c-Jun, c-Myc, c-Myb, CREB, and CEPBα. These diverse protein targets implicate GSK-3 in many aspects of cellular metabolism, proliferation, differentiation and development.
Currently, inhibition of GSK-3 may represent a viable strategy to develop novel medicinal entities for the treatment of such unmet diseases (Martinez A, Castro A, Dorronsoro I, Alonso M, Med. Res. Rev., 2002, 22:373-384) through insulin mimicry, tau dephosphorylation and amyloid processing, or transcriptional modulation respectively.
Among the great diversity of chemical structures with GSK-3 inhibition already found (Dorronsoro, I; Castro, A; Martinez, A Exp Opin Ther Patents 2002, 12:1527-1536; Alonso, M. and Martinez, A. Currrent Medicinal Chemistry 2004, 11, 753-761), the 2,4-disubstituted thiadiazolidinone (TDZD) are presented as the first ATP-non competitive GSK-3 inhibitors (Martinez A, Alonso M, Castro A, Perez C, Moreno F, J Med Chem, 2002, 45:1292-1299; WO 01 85685 and U.S. 2003/0195238). These compounds have great interest since they are selective and do not show inhibition on other several kinases such as PKA, PKC, CK-2 and CDK1/cyclin B. However, thiadiazolidinones have the tendency to react with nucleophiles and this property may jeopardize their drug potential.
There is still a need to find good GSK-3 inhibitors, being both effective and selective, and having good “drugability” properties, i.e. good pharmaceutical properties related to administration, distribution, metabolism and excretion.